1. Field of the Invention
The present invention relates to a glass-ceramics composite material. In detail, the present invention relates to a glass-ceramics composite material which has high thermal conductivity and is suitable for a low-temperature simultaneous firing use.
2. Description of Related Art
For example, in a wiring board applied to a semiconductor package, a multi-layer wiring board, etc., suppression of the loss by reduction of the electrical resistance of the conductor which constitutes wiring and improvement of the heat-resistance corresponding to the heat generated from a semiconductor element has been an important subject. As measures over the former, for example, low resistance metal (good conductor), such as gold, silver, copper, and an alloy containing such metal, is widely used as a conductor. On the other hand, as measures over the latter, a ceramic board which uses ceramics as a base is widely used in place of a resin board which uses resin as a base.
In such a ceramic board, as mentioned above, the conductor which constitutes a surface electrode and inner layer wiring comprises low resistance metal (good conductor), such as gold, silver, copper, and an alloy containing such metal, for example. Thereby, in such a ceramic board, For example, even in a case where highly fine-lined inner layer wiring is disposed for the purpose of improving the performance of a semiconductor package, etc., increase of the electrical resistance of the wiring can be suppressed and the resistance loss in the semiconductor package which uses the ceramic board can be reduced.
By the way, low resistance metal (good conductor), such as gold, silver, copper, and an alloy containing such metal, used for the purpose of suppressing increase of the electrical resistance of the wiring as mentioned above has a relatively low melting point as compared with other metal. When the sheet of dielectric material (base which consists of a dielectric layer) in which conductor pattern (wiring) comprising the metal having such a low melting point is embedded is simultaneously fired at the temperature more than the melting point of the metal, there is a possibility that the metal may melt and it may become difficult to maintain desired shape of the conductor pattern. Therefore, when using such a low resistance conductor as a conductor which constitutes a surface electrode and inner layer wiring, it is desirable to use the ceramics which can be fired at the temperature of less than the melting point of the low resistance conductor used.
In addition, as ceramics which can be fired at the temperature of less than the melting point of the low resistance conductor used as mentioned above, it is desirable to use what is called low-temperature firing board material (LTCC: Low Temperature Co-fired Ceramics). Even when low resistance metal (good conductor), such as gold, silver, copper, and an alloy containing such metal, which has a relatively low melting point as mentioned above, is used, a possibility that the metal may melt and it may become difficult to maintain the desired shape of the conductor pattern can be reduced.
By the way, for example, power semiconductor elements using, as a loss remedy, silicon carbide (SiC) wafers and/or gallium nitride (GaN) wafers which are being used widely in place of silicon (Si) wafers used conventionally have a feature that an operation at a higher temperature is possible, as compared with the power semiconductor element using the conventional Si wafer. Thereby, the cooling mechanism indispensable in the power semiconductor element using the conventional Si wafer (for example, a heat sink, a water-cooled mechanism, etc.) can be simplified drastically. As a result, reduction in size and weight of the power module can also be attained by using these new types of wafer.
However, the temperature in the surroundings of the power semiconductor element is becoming higher than before due to the rise of the operating temperature and reduction in size and weight of a power module as well as the simplification of a cooling mechanism accompanying use of the new types of wafer as mentioned above. Therefore, the demand for a ceramic board that has not only heat resistance higher than before, but also higher thermal conductivity, is increasing even more since the temperature of the surroundings of the power semiconductor element is becoming higher than before.
In the art, in response to such a demand, for example, it has been proposed to add particles having high thermal conductivity, such as aluminum nitride (AlN) particles and silicon carbide (SiC) particles, etc. (high thermal conductivity particles) as filler particles to the glass-ceramics composite material that constitutes the base of the ceramic board, which has an inner layer wiring consisting of low resistance metal (good conductor), such as gold, silver, copper, and an alloy containing such metal, for example (for example, refer to Patent Literatures 1 to 8).
Moreover, it has been proposed to blend a spinel system compound crystal phase such as gahnite (ZnAl2O4) and/or spinel (MgAl2O4), as well as at least one kind of non-oxide system compound crystal phase chosen from the group of aluminum nitride (AlN), silicon nitride (Si3N4), silicon carbide (SiC), and boron nitride (BN), into a glass phase comprising as a main component silicon oxide (SiO2), aluminum oxide (Al2O3), zinc oxide (ZnO), magnesium oxide (MgO), and boron oxide (B2O3), for the purpose of effectively raising the strength and thermal conductivity of a base (for example, refer to Patent Literature 9).
As mentioned above, in the art, various technology for raising the thermal conductivity of a glass-ceramics composite material have been proposed, for example, by adding a non-oxide system compound crystal phase, such as aluminum nitride (AlN), to a glass-ceramics composite material, as filler particles. Nevertheless, it is a fact that a glass-ceramics composite material having sufficient thermal conductivity has not yet been put into practical use by such conventional technologies.
As a cause inhibiting practical realization of the glass-ceramics composite material which has sufficient thermal conductivity, for example, the reaction between a non-oxide system compound crystal phase (filler particles), such as aluminum nitride (AlN), and a glass phase can be exemplified. When the reaction occurs, the non-oxide system compound crystal phase (filler particles) which has very high thermal conductivity (about 170 to 200 W/m·° C.) is consumed, and a spinel system compound crystal phase which has low thermal conductivity generates (specifically, about 20 to 25 W/m·° C. in the case of a spinel system compound crystal phase, and about 2 to 5 W/m·° C. in the case of silicate system oxides, such as mullite, cordierite, and magnesium silicate) generates. As a result, even when a non-oxide system compound crystal phase (filler particles) which has very high thermal conductivity is added, the effect on sufficiently raising the thermal conductivity of a glass-ceramics composite material is suppressed by the reaction.
Then, in the art, it has been proposed to suppress the reaction between a non-oxide system compound crystal phase (filler particles) and a glass phase by blending a specific rare earth component as an indispensable component into a glass phase (refer to Patent Literature 10). However, the producing district of rare earth is limited and there is uneasiness in the stability of supply and a price.
Therefore, in the art, there has been a demand for an easily-administered technology which demonstrates the intrinsic thermal conductivity improvement effect by addition of non-oxide system compound crystal phase (filler particles) and makes it possible to sufficiently raise the thermal conductivity of a glass-ceramics composite material.